Bispyridinium compounds as herbicides



United States Patent 3,458,305 BISPYRIDINIUM COMPOUNDS AS HERBICIDESWilliam Carter Doyle, Shawnee Mission, Kans., assignor to Gulf Research& Development Company, Pittsburgh, Pa., a corporation of Delaware NoDrawing. Filed Aug. 24, 1966, Ser. No. 574,541 Int. Cl. A01n 9/12; C07d99/10 U.S. Cl. 71-92 3 Claims ABSTRACT OF THE DISCLOSUREThiadiazolyleneand oxadiazolylenebis 4-pyridinium halides arepost-emergent herbicides which have improved selectivity when comparedto paraquat and are also useful as colored indicator reagents iniodometric analysis.

This invention is directed to the use of certain highly coloredbispyridinium compounds in which the two pyridinium salt structures areconnected by means of a divalent structure which contains a conjugatedsystem of valence bonds. These compounds, many of which are novel, maybe described as represented by the following structural formula in whichX is a halide ion, R is a hydrocarbon substituent group having amolecular weight less than about 150 and A is selected from divalentstructures represented by the formulas O S r u When R is a hydrocarbonsubstituent group with a molecular weight less than about 150, thesecompositions exhibit both good activity and selectivity, and are usefulin post-emergent control of broad-leaf weeds in crops such as corn,wheat, oats, and sorghum grains.

The general method of preparation of the thiadiazolylenebis compounds isillustrated by the following equation and Example I:

JL 1L 20H.

All temperatures given in the illustrative examples are in degreescentigrade.

Example I A quantity of 2,5-bis (4-pyridyl)-1,3,4-thiadiazole isprepared according to the procedure disclosed in J. Am. PharmaceuticalAssoc., vol. 42, p. 457 (1953). Then a slurry of 8.5 g. of 2,5-bis(4-pyridyl)-l,3,4-thiadiazole and ml. of dimethyl formamide at 50 isadded to 12.0 g. of methyl iodide and the mixture is stirred. Thestarting solid slowly dissolves, the solution becomes deep red and a redsolid begins to precipitate. After four hours at 50-55, the mixture iscooled to room temperature, filtered by suction and the solid washedwith acetone, giving 14.2 g. of 2,5bis (4-pyridyl)-1,3,4-thiadiazole bismethiodide, melting at 289-292 with decomposition. Dilution of thefiltrate by the acetone washings gives a second crop (2.6 g.) melting at292295 with decomposition.

The preparation of his methiodide compounds of this invention may berepresented as follows:

Example II Below are listed dimethyl bis methiodides prepared by thegeneral method of Example I, in which the divalent structure A isdifferent for each compound.

1 The 3,5-bis (4-pyridyl)-l,2,4-thiadiazole starting material wasprepared by the method disclosed in J. Am. Chem. 800., vol. 77, pg.4,062 (1955).

2 The free base employed as starting material is prepared according tothe procedure disclosed in I. Am. Chem. 800., vol. 81, pg. 962-6 (1959).

3 Example III Preparation of a higher alkyl bis quaternary compound isillustrated in the following equation:

Q Q 2nC H The procedure corresponding to the above equation is asfollows: A solution of 6.0 g. of 2,5-bis(4-pyridyl)-1,3,4- thiadiazoleand 11.0 g. of n-decyl bromide in 100 ml. of dimethyl formamide isheated 22 hrs. at 100-105 and cooled. Filtration of the precipitatedsolid and washing with acetone gives 5.9 g. of didecyl4,4-[2,5-(1,3,4-thiadiazol)ylene] bispyridinium dibromide, melting at245-7 with decomposition. Dilution of the filtrate by the acetonewashings precipitates an additional 3.9 g. of product melting at 246-8with decomposition.

Example IV In the following equation and table are listed otherthiadiazolylene bis quaternary ammonium salts prepared by the generalmethod of Example III s Cj Preparation of his quaternary ammoniumchlorides from corresponding iodides is illustrated below, employing aquarternary iodide prepared by the procedure of Example I from2,5-bis(4-pyridyl)-1,3,4-oxadiazole made according to the proceduredisclosed in Zhur. Obshchei Khim. vol. 30, p. 3240 (1960).

A solution of 10 g. of 2,5-bis (4-pyridyl)-1,3,4-oxadiazole bismethiodide in 50 ml. of water is stirred /2 hour with 50 g. of a strongbase anion exchange resin (chloride form). The slurry is filtered, theresin is washed with 50 ml. of water and the aqueous filtrate is pouredinto 600 ml. of acetone, precipitating a yellow solid. Filtration ofthis solid and washing with acetone gives 4.6 g. of 2,5-bis(4-pyridyl)-l,3,4-oxadiazole bis methochloride, melting at 255-8 withdecomposition.

4 Example VI Using the procedure illustrated in Example V, 2,5-bis-(4-pyridyl)-1,3,4-thiadiazole bis methiodide is converted in 65% yieldto the corresponding bis methochloride, melting at 285-8 withdecomposition.

Example VII The novel bis quaternary salts of the present invention showa variety of interesting color reactions in aqueous solution which areuseful in analytical chemistry; those which are particularly interestingand useful including 1) an intense green coloration in the presence ofstrong reducing agents such as zinc dust and sodium dithionite, thecolor being discharged reversibly by bubbling air through the solution;(2) a strong red color in the presence of primary and secondaryaliphatic amines and (3) on increasing the pH of the solution, an abruptchange from colorless to yellow at around pH 7-8 with a gradual changeto orange at higher pH values (both of these color changes arereversible).

The color change in (1) above may be used to indicate the end point inanalytical titrations using strong reducing agents. For example, thetitration of commercial sodium hypochlorite bleach solution with sodiumthiosulfate in the presence of 2,5-bis(4-pyridyl)-1,3,4-oxadiazole bismethochloride shows a sudden change from colorless to green at anend-point corresponding to 4.6% NaOCl in the bleaching solution. Sincethe standard iodometric titration of the same solution gives a value of4.87 percent, the new reagent yields a reference point prior to completereduction. The end point appears to be sharply defined and relativelystable on exposure to the atmosphere.

The new compositions yield accurate determinations of equivalence pointin the titration of a strong acid with a strong base, as illustratedbelow:

A 20.0 ml. portion of 0.1003 N H is diluted with 50 ml. distilled water,20 drops of a solution of 0.02 g. of 2,5-bis(4-pyridyl)-1,3,4-oxadiazolebis methochloride in 10 ml. water is added and the solution is titratedwith 0.0997 N NaOH. A sharp color change from colorless to yellow occursafter the addition of 20.61101 ml. of the titrant.

In the discussion below there is illustrated the use of the novelcompositions as selective post-emergence herbicides.

The species of plants on which the compound was to be used were plantedin four-inch pots in the greenhouse. Ten to eighteen days afteremergence of the plants, three pots were sprayed with each aqueousdispersion of active agent, prepared as follows: An emulsifiableconcentrate was made by combining 0.4 g. of the chemical to be testedwith 4 m1. of a solvent-surfactant mixture (3 parts of polyoxyethylatedvegetable oil and 1 part kerosene or other hydrocarbon solvent). Theemulsifiable concentrate was then mixed with a suitable amount of water,with agitation, so as to provide a convenient concentration for theparticular application rate. Various rates of application of the activechemical per acre were employed as indicated in the table at a sprayvolume of about 60 gallons per acre. Approximately one week after thespray application the plants were observed and the results ratedaccording to the following schedule:

Type of action: Degree C=chlorosis (bleaching =no eifect.

=necrosis 1=slight efifect. G=growth inhibition 2=moderate effect.F=formative eifect (abnormal form of growth) 3=severe effect.K=non-emergence 4=maximum eifect (all plants died).

Results are tabulated below.

In a field test of the compound of Example I in comparison with paraquatusing the same spray formulation as in the greenhouse tests, the new bisquaternary compound successfully controlled broadleaf weeds, includingpigweed and morning glory, with only slight effect on corn and milo atan application rate of /2 lb. per acre. In the same test at the sameapplication rate, paraquat gave a non-selective, complete kill of allvegetation. The phytotoxic selectivity which is characteristic of thenew compositions makes them particularly useful as herbicides forcontrol of weeds in grain crops. The dimethyl 4,4'-[2,5-(1,3,4-oxadiazol)ylene] lbispyridnium chloride is particularly useful ina method of combating weeds in a heavily weed-infested area, while atthe same time raising a crop of grain sorghum (milo) on the land. Byrepeated use of the method on the same land the concentration of viableweed seeds in the soil will eventually be reduced to a normal level,without the soil being rendered unusable for a period of time, as occurswith drastic methods of dealing with heavy weed infestations.

What is claimed is:

1. The method of combating weeds which comprises applyingpost-emergently to the weeds a herbicidally effective amount of acompound represented by the formula in which X" is selected from Cl,Brand I", R is a substituent group selected from benzyl and alkyl havinga molecular weight less than about 150 and A is selected from divalentstructures represented by the formulas tit tilt m 2. The method ofcombating weeds which comprises applying post-emergently to the weeds aherbicidally effective amount of a compound represented by the formulain which X is selected from Cl", Brand I- and R is a substituent groupselected from benzyl and alkyl having a molecular weight less than about150.

3. The method of combating weeds which comprises applyingpost-emergently to the weeds a herbicidally effective amount of thecompound represented by the formula References Cited RICHARD L. HUFF,Primary Examiner G. HOLLRAH, Assistant Examiner US. Cl. X.R.

